1. Field of the Invention
The present invention relates to a camera system having the function of automatically adjusting parameters relating to image taking, and to a camera used for the camera system, an accessory used for the camera system and a lens apparatus used for the camera system.
2. Description of Related Art
Conventionally, a focus detection method based on TTL phase-difference detection has been generally used in lens exchangeable single-lens reflex camera systems. However, it is difficult to completely match a focus position detected by this phase difference detection to the actual surface to be focused.
This is due to factors such as errors occurring at the time of mounting a sensor module employing phase difference detection on a camera body, errors on the side of a camera body such as the dimensional errors of an optical system constituting the sensor module, and manufacturing errors in an image-taking lens manufactured separately from the camera body.
As a method for correcting manufacturing errors, Japanese Patent Application Laid-Open No. 2000-292684 discloses a method for correcting errors on the side of the camera body. This method uses a first focus detection unit employing phase difference detection and a second focus detection unit for autofocusing by evaluating the contrast from an image signal of the image-pickup element, calculates a relative displacement amount from autofocus data obtained by the first and second focus detection units, and corrects the autofocus data of the first focus detection unit.
In the case of single-lens reflex camera systems, several types of lens apparatuses can be mounted. Naturally, each lens apparatus has a different amount of manufacturing errors, resulting in the problem of focus position displacement of the image-taking lens.
One method for solving this problem is performing focus correction for each lens apparatus. More specifically, after performing image-taking with the focus position displaced slightly backward and forward from the focus position set at the time of manufacturing, the obtained image which best matches with a target focus position set by the user is selected, and the focus position is corrected using the relative displacement amount as an AF correction value.
However, the above-described conventional camera system has the following problems. In the case of the camera system disclosed in Japanese Patent Application Laid Open No. 2000-292684, the displacement of the focus position caused by manufacturing errors can be corrected for a combination of a single type of lens apparatus and a camera. However, in the case of a single-lens reflex camera, on which a plurality of lens apparatuses can be mounted, the correction is not performed when the lens apparatus is changed, resulting in the problem of focus position displacement. Japanese Patent Application Laid Open No. 2000-292684 does not disclose any measures against this problem.
On the other hand, this problem can be solved in the above-described method in which focus correction is performed for each lens apparatus. However, when the user has several cameras and lens apparatuses, the user may perform image-taking not knowing whether the displacement amount of the focusing surface is corrected in the combination of camera and lens apparatus used during the image-taking, resulting in the problem that focusing has not been established.
Furthermore, if focus displacement is confirmed after performing image-taking, this also results in the problem that the user cannot determine whether the camera system requires focus position adjustment or whether there is a defect.
On the other hand, Japanese Patent Publication No. H7(1995)-117677 discloses a technique for storing in advance adjustment values for performing predetermined operations for various functions such as an autofocus adjustment function and an auto exposure function. More specifically, Japanese Patent Publication No. H7-117677 discloses a method of incorporating an adjustment program for an auto exposure function in a camera, causing the camera to detect individual differences among products when a calibration signal indicating that the camera is in a calibration step is supplied, to write an adjustment value corresponding to the individual operation characteristics in a nonvolatile memory, and to execute an adjustment operation.
This method is aimed at detecting, in a calibration step, individual differences among products resulting from discrepancies and the like of the components during manufacturing, storing adjustment values corresponding to the operation characteristics of each product at the time of factory shipment, and performing an appropriate operation during image-taking, based on the adjustment data.
Additionally, Japanese Patent Application Laid-Open No. 2001-174690 discloses a camera which allows the user to freely correct an adjustment value set in a calibration step at the time of factory shipment and to freely restore the setting made at the time of factory shipment, by using a first storage section which stores an adjustment value set in a calibration step, a second storage section which stores a correction value for correcting the adjustment value stored in the first storage section and a modification section which modifies the correction value stored in the second storage section according to the user's intention.
However, in the autofocus adjustment of a lens exchangeable camera, to which a plurality of lens apparatuses having different functions are selectively mounted, the same correction is performed for all the lens apparatuses mounted on the camera. For example, in the case where a plurality of lens apparatuses of the same type are mounted on the camera, the same correction is performed for all the lens apparatuses.
This method can solve the problem when the discrepancies of all the mounted lens apparatuses are sufficiently small and the camera requires calibration. On the other hand, when the lens apparatuses mounted require calibration, calibration has conventionally been performed for the lens apparatuses.
When the discrepancy of both the camera and the lens apparatuses are sufficiently small, it is not necessary to perform calibration for a general practical use in the above-described conventional technique. However, higher focusing accuracy is required for taking special purpose photographs, such as commercial photographs, which need to be enlarged to very large sizes. To perform such a fine-tuning, it is also necessary to take into account discrepancies which occur only when a specific camera and a specific lens apparatus are combined.
That is, for example, even lens apparatuses of the same type have different setting angles with respect to a mount disposed in front of the camera, so that it is necessary to eliminate such minute discrepancies resulting from difference in the setting angle, in order to achieve higher focusing accuracy.